Activated carbon is normally used to absorb and separate contaminants from liquids or gases flowing through the activated carbon. The majority of activated carbon is used to absorb materials from liquids in so-called "wet" applications. In a typical wet adsorption process, the activated carbon is formed into a bed in an adsorption vessel chamber, and the liquid to be treated is flowed through the bed. Materials in the liquid adhere to the surface of the activated carbon and remain in the carbon bed while the liquid flows through the bed and out of the vessel.
Eventually, the activated carbon used in adsorption systems becomes spent. Spent carbon may be replaced by new activated carbon or regenerated activated carbon. It is often more economical to regenerate the spent activated carbon than to replace the activated carbon with new material. Generally described, the regeneration of activated carbon involves heating the carbon to about 800.degree. to 1000.degree. C. in a furnace or kiln in a reducing environment which is normally steam. However, current activated carbon regeneration systems also must use a substantial amount of auxiliary equipment for carbon handling and environmental control.
Activated carbon regeneration may be conducted at the adsorption site or at a regeneration site remote from the adsorption site. Off-site regeneration is preferred for many activated carbon users, especially users of relatively small amounts of activated carbon, because of the large capital expense required in constructing a regeneration facility, relatively infrequent use of the regeneration facility by a single activated carbon user, environmental regulations which must be followed, and the knowledge and experience required to operate a regeneration facility.
Current environmental regulations dealing with activated carbon regeneration set forth many requirements, but one of the more significant requirements is that the whereabouts of the spent activated carbon, particularly activated carbon containing hazardous waste, be monitored. When off-site activated carbon regeneration facilities are used, monitoring the location of the activated carbon becomes more difficult, because the spent activated carbon must be transported from the adsorption site to the regeneration site. The spent activated carbon is then normally stored until it can be sent through the regeneration process. When hazardous wastes are involved, the spent activated carbon must be regenerated without being intermixed or commingled with other spent activated carbons. Thus, additional storage facilities at the regeneration site are required. In addition, monitoring the location of the spent activated carbon is difficult when the regeneration facility has a complicated carbon handling scheme.
Conventional activated carbon regeneration systems include a substantial amount of auxiliary equipment in addition to the kiln in which the activated carbon is actually regenerated. This auxiliary equipment is mostly used for carbon storage and handling and for environmental control. For example, most conventional activated carbon regeneration systems include a relatively complicated carbon storage and transfer system wherein the carbon is conveyed by means of a liquid transport medium such as water. Typically, the spent activated carbon is delivered in a bulk trailer to the regeneration site. The carbon is removed from the bulk trailer, mixed with water to form a slurry, and pumped to a surge tank for storage. When the regeneration system can receive the spent activated carbon, additional water is used to pump the spent activated carbon from the storage tanks through a series of surge tanks and dewatering screens to a thermal dryer, wherein the spent activated carbon is dried before being reactivated in a kiln. After regeneration, the activated carbon is normally stored in another surge bin system before being loaded into a bulk trailer and transported back to the adsorption site.
The use of water slurries to transfer carbon in activated carbon regeneration systems causes several problems. For example, the water used to form the slurries and transport the carbon must be treated in an environmentally sound manner. This water treatment requires equipment, thus adding to capital costs. The carbon handling and water treatment equipment in a conventional activated carbon regenerated system often amounts to about 25 percent of the total capital costs of the conventional activated carbon regeneration system. There has been a desire to cut these costs because the carbon handling and water treatment equipment is not directly involved in the activated carbon regeneration process. In addition to the high capital cost, the carbon handling and water treatment portion of a conventional activated carbon regeneration system is responsible for a significant amount of operating costs. The operating costs include manpower, the water itself, and energy to move the water and the water-carbon slurries and to dry the carbon. Furthermore, relatively fine activated carbon particles are lost through the dewatering screens in the carbon handling portion of a conventional regeneration system. The mechanical agitation involved in the slurry handling causes breakdown of the activated carbon particles, further magnifying the problem. The lost carbon must then be replaced with new carbon, which further adds to the overall cost of the process.
Another problem with the use of water as a transport medium in conventional regeneration systems is the difficulty in tracking the carbon as it is run through the slurry system, making compliance with environmental regulations more difficult. As set forth above, one must take care not to allow carbon containing hazardous waste to mix with and contaminate other carbon. One must also take care not to allow water leakage from the system. When hazardous wastes are involved, slurry water leaks can become a serious environmental control problem.
Therefore, there is a need for an activated carbon regeneration system with a simplified carbon handling scheme so that activated carbon can be more economically regenerated and environmental regulations associated with activated carbon regeneration can be more effectively achieved.